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PLANTING TOO DEEP #1 CAUSE OF TREE FAILURE
If you plant trees this spring, or hire someone to plant trees for you, make sure the trees get planted at the correct depth. Far too many trees are planted too deep.
I recently completed 30 hours of training at the University of Minnesota to become a Tree Care Advisor (TCA). The five Saturday sessions covered tree and shrub selection, urban soils, insects, disease, proper planting, pruning, and evaluation of hazard trees.
I mention this only to make a point - the TCA training convinced me beyond any doubt that the leading cause of tree failure is planting too deep. Nearly every tree problem we discussed seemed to have some connection with planting too deep.
Trees that are planted too deep usually die a premature death - they tend to reach the end of their lifecycle many years ahead of their potential life span. Some of the problems that result from too-deep planting include:
- Restriction of water and oxygen to the fine root system
- High incidence of stem cankers and decay
- Poor root system regeneration
- Gradual death of existing roots
- Extended period of transplant shock
- Reduced tree vitality and reserve of energy
- Increased vulnerability to insects, disease, drought, flooding and wind
- High incidence of adventitious roots (i.e., new, abnormal root growth from the buried portion of the stem). These adventitious roots often become encircling and girdling roots that choke the tree by constricting the movement of moisture and nutrients.
Before discussing why and how trees get planted too deep, we need to understand what is the proper planting depth.
The spot at the base of the trunk of every tree where the largest roots begin extending outward is the root crown (also called "root collar"). This root crown should be planted at landscape grade or slightly above landscape grade. Sadly, the root crown often gets buried anywhere from 1 inch to a foot below the soil surface.
A tree that is planted too deep can reveal its plight by exhibiting a variety of symptoms. These include nutrient deficiencies, leaf scorch, leaf wilt, branch tip die-back, stunted growth of leaves and branches, early fall coloration and premature leaf drop, and a gradual decline in appearance.
If you have trees in your yard that you suspect may be planted too deep, you can do your own root collar examination. Using a shovel and trowel, dig away the soil at the base of the trunk. As you dig, be careful not to damage stem bark or root tissue. Keep digging down until you locate the root collar - the first roots that branch out laterally from the trunk. If you see these roots at landscape grade, your tree is planted at the right depth. If you find these branch roots down one inch or deeper below landscape grade, your tree is planted too deep.
If the tree has only been in the ground for a year or two, you may still be able to partially rectify the problem by removing soil down to the level of the root collar and replacing the removed soil with mulch. The mulch should not be mounded up tight against the trunk.
Why are trees often planted too deep? One of the most common causes is the way trees are raised in many nurseries. It is a common practice in some nurseries to cultivate around trees to control weeds. This mechanical procedure "hills up" soil against the trunks of trees and gradually raises the grade above the root collars.
Later, when the nursery digs these trees and creates the burlap-covered root balls, the extra soil above the root collar becomes part of the root ball. If the installation contractor simply plops a B&B root ball into the hole so that the top is level with landscape grade, the root collar may get planted below grade.
Many hybrid trees are accidentally planted too deep. Hybrid trees are the result of a graft of one species onto the stem of another species. This practice is common with many fruit trees and an increasing share of shade trees. The grafting process creates a bulge on the stem where the graft occurred. Some people mistake this enlarged graft area for the root collar and plant the tree so the graft is at landscape grade. As a result, this tree gets planted 6 inches to a foot too deep.
Some people plant trees too deep because they think "deeper is better." Or they misjudge the height of the B&B or container root ball. By the time the heavy ball gets dropped into the hole, they realize too late that the hole was dug too deep.
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